Vulcanization of copolymers of conjugated diene hydrocarbons and alpha-methylene nitriles



Patented Apr. 24, 1945 VULCANIZATION OF COPOLYMERS OF CON-1 JUGATED .DIENE HYDROCARBONS .AND; ALPHA-METHYLENE NITRILES Doran E. Sauser, Cuyahoga Falls, Ohio, assignor,

by mesne assignments, to The B. F.-Goodrich Company, Akron, Ohio, a corporation of New a York No Drawing. Application May 17,1941,

Serial No. 394,036

Claims.

This invention relates to the vulcanization of copolymers of conjugated diene hydrocarbons and alpha-methylene nitriles. and has as its principal object to providea vulcanizing agent which may be substituted for sulfur wholly or in part to produce vulcanizates having improved physical properties such as tensile strength and elongation.

It has previously been proposed to vulcanize natural rubber in the presence of bis oXythiono polysulfides. Thes materials are not particularly useful in natural rubber, however, unless-sulfur andan aniline type accelerator are employed in conjunction therewith. Use of bis o xythiono), polysulfides as a replacement. for sulfur in natural rubber produces vulcanizates of inferior physical properties.

I have now found that when bis(oxythiono) clohexyl oriythionoli tetrasulfide, .bis l benzyloxythiono) tetrasulfide bis ('allyloxythiono) tetrasulfide. bis(isopropenyloxythiono) tetrasulfide. and the correspondingtrisulfides.

The synthetic rubbers with which. this invention is concerned are formed. by the copolymerization, preferably in the form of an aqueous emule sion, of a conjugated dien hydroc r on such a butadiene (by which is .meanthutadiene-l, 3), isopre e, x-d hy u a ne. n er lene, et with an alphamethylene nitrile, by which is meant nitriles containing a methylene group attached to. the carbon atom adjacent. to the polysulfides' are employed as vulcanizing agents,

as distinguished from accelerators, in synthetic rubbers prepared by the copolymerization of a conjugated dienehydrocarbon and an alphamethylene nitrile, vulcanizates having greatly improved physical properties are produced.

Bis(ox ythi0no) polysulfides are a class of compounds which may be represented by the struc tural' formula In'the preferred compounds R1 and R2 represent the same or difierent functionally aliphatic groups such as alkyl, alkenyl, aralkyl, or cycloalkyl groups. The trisulfides, wherein a: represents' 1, may be prepared by the reaction of an alkali metal xanthate with sulfur dichloride, while the' tetrasulfides, wherein :0 represents 2, may be prepared by the reaction of an alkali metal xanthate with sulfur monochloride. Other polysulfides of unknown structure containing a higher proportion of sulfur than the tetrasulfides are also Within the scope of the invention. In general, however,' the bis(alkoxythiono) tetrasulfides are found to be most suitable for use on a commercial sale. Specific compounds which may be employed as vulc'anizing agents include bis- (methoxythiono) tetrasulfide, bis(ethoxythiono) tetrasulfide, bis(n-propoxythiono) tetrasulfide, bis (isopropoxythiono) tetrasulfide, bis (n-butoxythiono) tetrasulfide, bis(isobutoxythiono) tetrasulfide', bis(sec-butoxythiono) tetrasul fide, bis- (terbutoxythiono) tetrasulfide, bism-amyloxythiono)" tetrasulfide, bis(pri-act-amyloxythiono) tetrasulfide, bis(sec-act-amyloxythiono) tetrasulfide; bisfter-amyloxythiono) tetrasulfide, bis(cy- CEN group, such as acrylonitrile, alphaemethe acrylonitrile, alpha-ethacrylonitrile, alpha-methoxymethacrylonitrile, alpha-chlorrnethylacrylonitrile, etc. The nitrileis preierably employed in a sma er a unt. than the diene. althou h the use. of gr ate amounts o nitrile. roduces compositions..whicl1 can be vulcanized byv the method. her n cri ed o r u e. ompositions resembling leathe ra her than rub r.

As. a specifloexa nple 0f on em diment of this invention. I l -show e man er n w ich on of the ,vulcanizing agents of thisvinvention may be employed in a pur um? st ck. a composition containing no fillers or reinforcing ,pige ments or. only insignificant. amounts thereof.

\ Synthetic rubber prepared by the emulsion Gopolymerization of parts by weight ofbutadiene and 45 parts oracrylonitrilewas mixed with 5 parts of zinc oxide, 1.5; parts ofstearic acid, 1.25 parts of an accelerator consisting of. a mixture of approximately parts of 2-mercapto4., 5-dimethylthiazole and 2 parts f -m rcapt -ihylth aZ'Ole and parts of sulfur. When the com.- position was, heated in .a press for SQminutes at 310 F., a vulcanizate having a tensile strength a of 1100lbs./in. and an elongation of 550% was produced. When l part of bis(isopropoxythiono) tetrasulfide' was substituted for the sulfur inthe above recipe, a "vulcanizate having a tensile strength of 2000 lbs/in. and an elon ation of 880% was produced. "The use of 3,68 parts of bi s(isopropoxyth iono) te'trasulfide (an amount which is found upon analysis to contain 1.25 parts of free sulfur) produced a vulcanizate having a. tensile strength-of 3 125 lbs/in} and an elongation of 670%. 1 V

In another example, 'l0'0 parts of the, copolymer of butadienehnd acrylonitrile known commercially as Perbun'an were employed as the synthetic rubb'er"in the above pure gum stock. The vulcanizate prepared with sulfur as the vulcanizing agent had a tensile strength of 1'50 lbs/in. and an elongation of 390%, while the vulcanizate prepared with bis(isopropoxythiono) tetrasulfide had a tensile strength of 1025 lbs/in. and an elongation of 600%.

In another example, a composition suitable for the manufacture of printing rolls was prepared by vulcanizing a mixture of 100 parts of an emulsion copolymer of butadiene and acrylonitrile, 25 parts The vulcanizing agents herein described may, .be employed in widely varying proportions. The

use of from .5 to %based on the synthetic rubber is ordinarily suflicient, although greater or less amounts may be employed in some cases. While it is preferred to use a bis(oxythiono) polysulfide as the sole vulcanizing agent, the advantages ,herein described. will be obtained to some extent only 400 lbs/in. and an elongation of 430% was;

produced.

Thiazole-type accelerators, by which s meant accelerators deriving at least part of their activity from the presence of a substituted Z-thiothiazylf group, such as the mixture of i2-mercapto-4,5-

dimethylthiazole and 2-mercapto-d-ethylthiazole employed above are the preferred accelerator for use with the vulcanizing agentsofthis invention. Other suitable thiazole-type acceleratorsbesides the z-mercaptoalkylthiazoles mentioned above are the aromatic. 2-mercaptothi'azoles. such as 2- mercaptobenzothiazole, 2 --.mercap'tonaphthothiazole, 2-mercaptotoluothiazole; 5 the thiazyl di sul fides such as di-Z-benzothia'zyl disulfide, di-2- (4-- etl'lylthiazyl) disulfide, (ii-2 14.5-dimethylthiazyl) disulfide; and theamino thiazyl sulfides such as 2-benzothiazyl diethylamino sulfide, 2-(4 -ethyl-, thiazyl) cliethylamino sulfide,'. 2 benzothiazyl cyclohexylamino sulfide, etc. A o

It is within the scope of the invention, however. to employ other types of accelerators such'as the aldehyde-amine condensation products which possess accelerating activity suchfasfpolybutylidene aniline; methyleneparatoluidine, etc.; the dithiocarbamate such as zinc dimethyldithiocarbamate', zinc phenvl-beta-naphthyl dithiocarbamate, etc.: the thiuram sulfides such as tetramethyl thiuram 'm0nosulfide,.. tetramethyl thiuram disulfide, etc; and the uanidine accelerators such as diphenyl guanidine. di-orthotolyl guanidine, etc. s v L As an example ofthe'useof anothentype of accelerator, a mixture of IOOparts-of anemulsion copolymer. of .55 parts of butadiene, and 45 parts .of acrvlonitrile, 5 parts of zinc oxide.-1.5 parts of stearic acid, 1.25 parts of di-ortho-tolylguanidine, and 3.68 parts of bis(isopropoxythiono) "tetrasulfide was heated in a press for 30 minutes at 310 F. The-vulcanizate had a tensile strength of 2500 lbs. /in. and an elongation of 800%. These values are muchhigher than those :exhibited by pure gum stocks vulcanized with sulfur as a vulcanizingagent.

Although the use of the -bis(ox vthiono) polysulfides in the specificexample has-been confined to pure gum stocks and-printing roll compositionsthe vulcanizingagents herein described may be similarly employed in any type of-rubber composition such as-those used-for automobile tires and tubes, hose, belting, sheet and thread rubber. rubberized fabrics, molded goods, seamless dipped goods, boots and shoes,.etc.,whether vulcanized in a heated mold, in open steam, in hot air, in hot water; etc. The vulcanizing agents may be incorporated in the synthetic rubber while the rubber is being worked on a roll mill or masticated in an internal mixer, and the vulcanizing agents may be added'alone, or in adwhen sulfur or another vulcanizing agent is only partially replaced by a bis(oxythiono) polysulfide. .It is accordingly within the scope of the invention to add to the rubber before vulcanization both sulfur and a bis(oxythiono) polysulfide, although it is preferred to perform the vulcanization in the absence of any added elemental sulfur.

It may also be desirable in some instances to yulcanize a mixture of a. copolymer ofbutadiene and acrylonitrile and natural rubber. Although the bis(oxythiono).polysulfldes are not as satisfactory vulcanizing agents as sulfur in natural rubber, it will be found. advantageous to employ the polysulfides when minor proportions of natural rubber are present in the synthetic rubber. i

While I have herein disclosed certain specific embodiments of my invention, I do not intend-to limit the invention solely thereto, for many modifications including substituting materials having equivalent properties and varying the proportions of materials used are within the spirit and scope of theinvention as defined in the appended I claim: r l

1. The method which comprises vulca-nizing a copolymer of a conjugated dienehydrocarbon and an alpha-methylene nitrile in the presence oi. a vulcanizing agent comprisinga bismxythionol polysulfide. a r l 2. The method which comprises vulcanizing an emulsioncopolymer of butadiene and asmaller amount ,of an alpha-methylene. nitrile-ingthe presence of a vulcanizing agent consisting ofa bis(oxythiono) polysulfide in the absence of any added elemental sulfur.

3. The method which comprises vulcanizing an emulsion copolymer of butadiene and a smaller amount of acrylonitrile in the presence or a vulcanizing agent comprising a bis(alkoxythiono) tetrasulfide.

4. The method which comprises vulcanizing an emulsion copolymer of butadiene and a smaller amount of acrylonitrile in the presence of a vulcanizing agent consisting of a bis(alkoxythiono) tetrasulfide'in the absence of i any added elemen tal sulfur.

5. The method which comprises vulcanizing an emulsion copolymer' of butadiene and a smaller amount of acrylonitrile in the presence of a vulcanizing agent consisting of a bis(alkoiiythiono) tetrasulflde, and a acceleratordriving at least part of its activity from the presence oi. 'a 2- thiothiazyl group, in the absence of any added elemental sulfur.

6. The method which comprises vulcanizing an emulsion copolymer of butadiene and a smaller amount of acrylonitrile' in the presence of a' vulcanizing agent consisting of a bis(alkokythioho) tctrasulfide, and a 2-mercapto alkyl-thiazole. V

'7. The method which comprises vulcaniz'ing. an emulsion copolymer of 55 partsof butadiene and 45 parts ofacrylonitrile in the presence'of'a vul claims.

canizing agent comprising a bis(oxythiono) polysulfide.

8. The method which comprises vulcanizing an emulsion copolymer of 55 parts of butadiene and 45 parts of acrylonitrile in the presence of a vulcanizing agent consisting of bis(isopropoxythiono) tetrasulfide and an accelerator comprising 2-mercapto-4,5-dimethyl thiazole, in the absence of any added elemental sulfur.

9; The method which comprises vulcanizing an emulsion copolymer of butadiene and a smaller amount of acrylonitrile in the presence of a vultetrasulfide.

10. A vucanizate prepared by the method 0t claim 1.

11. A vulcanizate prepared by the method of claim 3.

claim 5.

13. A vulcanizate prepared by the method of claim 6.

14. A vulcanizate prepared by the method of 10 claim 7.

15. A vulcanizate prepared by the method of claim 9.

DORAN E. SAUSER. 

